Ultraviolet light activated oxidation process for the reduction of organic carbon in semiconductor process water

ABSTRACT

In a system for decomposing organic compounds in water for use in semiconductor manufacturing, a chemical reactor vessel having a fluid inlet and a fluid outlet, a persulfate anion addition system upstream of the reactor vessel, and a light emitting device contained within the reactor vessel. The light emitting device provides light capable of decomposing persulfate anions.

RELATED APPLICATIONS

This application is a continuation-in-part of pending U.S. patentapplication Ser. No. 12/303,596, filed Dec. 5, 2008, and titledULTRAVIOLET LIGHT ACTIVATED OXIDATION PROCESS FOR THE REDUCTION OFORGANIC CARBON IN SEMICONDUCTOR PROCESS WATER, which patent applicationis a national stage entry under 35 U.S.C. § 371 of PCT/US07/70416 filedJun. 5, 2007, and titled ULTRAVIOLET LIGHT ACTIVATED OXIDATION PROCESSFOR THE REDUCTION OF ORGANIC CARBON IN SEMICONDUCTOR PROCESS WATER whichclaims priority to U.S. Provisional Application Ser. No. 60/811,220filed Jun. 6, 2006, and titled ULTRAVIOLET LIGHT ACTIVATED OXIDATIONPROCESS FOR THE REDUCTION OF TOTAL ORGANIC CARBON IN ULTRAPURE WATER,which patent applications are hereby incorporated herein by reference intheir entireties for all purposes.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to a process for thepurification of water used in semiconductor manufacturing. Morespecifically, the present disclosure relates to a process that usesultraviolet activated persulfate to decompose organic compounds in bothpure and spent process water streams in semiconductor manufacturingfacilities.

BACKGROUND

Reducing TOC in water using ultraviolet light activated aqueouspersulfate is known. It is an established method of decomposing organiccompounds in water and is discussed in, for instance, U.S. Pat. No.4,277,438, to Ejzak, which teaches a batch process of preparing watersamples for the measurement of TOC by: (1) persulfate addition, (2)irradiation with an extreme dose of UV (which also heats the sample) toactivate the persulfate to oxidize any TOC to carbon dioxide and water.U.S. Pat. No. 5,443,991, by Godec et al, teaches a similar method.

U.S. Pat. No. 5,571,419, to Obata et al, discloses a method of producingUltra Pure Water (UPW) having a low concentration of organic matter. Thepurification method requires the following process for the water to betreated: (1) pH adjustment to less than 4.5, (2) addition of anoxidizing agent (such as a persulfate salt), (3) heating of the water topreferably a minimum of 110° C. and more preferably to 120° to 170° C.,and (4) cooling the water to the temperature required for use.

The prior art also includes references showing an advanced oxidationprocess to destroy organic compounds in wastewater, including U.S. Pat.No. 5,762,808, to Peyton, and U.S. Pat. No. 6,096,283 to Cooper et al.

However, despite improvements in this technology, there remains a needfor an improved method of producing a reliable, continuous source of lowTOC UPW for the semiconductor industry and other industries that requireultrapure water with controlled total organic carbon. The presentdisclosure describes UV activation of persulfate salt to produce highoxidation potential radicals at ambient temperature, in non-pH adjustedwater to purify UPW prior to discharge from the Point of Distribution(POD), prior to the Point of Connection (POC) (typically labeled as thePoint of Use or POU), and to purify spent UPW for reuse on a continuousbasis.

SUMMARY

This disclosure is a process used for the decomposition ofcarbon-containing compounds in water. This process reduces total organiccarbon (TOC) in water through the addition of a persulfate salt upstreamof an ultraviolet light source. The ultraviolet light is absorbed by thepersulfate—converting the persulfate into sulfate radicals. The sulfateradicals oxidize TOC, converting the contributing compounds into CO2 andmineral salts.

This disclosure describes the use of the UV/persulfate oxidation processfor the purification of water used in semiconductor manufacturing andthe production of UPW in general.

The process uses a standard photochemical reactor either a plug flow(PFR) or a stirred tank (CSTR) or a combination of both. The mostcost-effective design is expected to be a CSTR with immersed UV lamps.Multiple reactors can be used in series to improve reagent utilization.

A method of reducing TOC in semiconductor process water is disclosed.

Other features of the disclosure, regarding organization and method ofoperation, together with further objects and advantages thereof will bebetter understood from the following description considered inconnection with the accompanying drawings, in which embodiments of thedisclosure are illustrated by way of example. It is to be expresslyunderstood, however, that the drawings are for illustration anddescription only and are not intended as a definition of the limits ofthe disclosure. The various features of the disclosure are pointed outwith particularity in the claims annexed to and forming part of thisdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood and objects other than thoseset forth above will become apparent when consideration is given to thefollowing detailed description thereof. Such description makes referenceto the annexed drawings wherein:

FIG. 1A is a schematic view of an advanced oxidation system inaccordance with one or more embodiments;

FIG. 1B is a block schematic diagram of a semiconductor industry UPWsystem showing possible locations in which the advanced oxidation systemcould be employed in accordance with one or more embodiments;

FIG. 2 is a graph showing the absorption spectrum for aqueouspersulfate;

FIG. 3 is a graph showing the effect of urea concentration ondecomposition performance for plug flow reactor, with persulfate at 0.5ppm and a 0.9 minute residence time; and

FIG. 4 is a graph showing the results of a simulated pilot test of thesystem to treat spent rinse water in accordance with one or moreembodiments.

DETAILED DESCRIPTION

Referring to FIGS. 1 through 4, wherein like reference numerals refer tolike components in the various views, FIG. 1A is a schematic viewshowing the elements comprising the UV activated oxidation process forreducing organic carbon in semiconductor process water, generallydenominated AOP 100 herein. TOC decomposition performance is controlledby the size of the reaction vessel, the intensity and amount of UV lightused, and the amount of persulfate injected. The system configurationincludes a source of untreated water 110, which is fed into a chemicalreactor vessel 120 through one or more fluid inlets 130. Persulfate froma persulfate anion addition system 140 is also fed into the reactorvessel, the system including a persulfate feed tank 150, a fluid inlet160, and a feed pump 170. One or more UV lights 180, 190 are disposedwithin the vessel enclosure, as is a chemical solution mixer 200.

The reactor vessel may be a continuous-stirred tank reactor (CSTR). Thiskeeps down cost and increases system simplicity. However, a plug flowreactor (PFR) may be preferred in situations where space (systemfootprint) is at a premium. Alternatively, a CSTR can be used in serieswith a PFR 210 having UV lights 220 to increase system efficacy.

The treated water is discharged either directly (in the case of a singlereactor system) through one or more discharge outlets 230 for furtheruse, or into the PFR for further treatment and subsequent discharge froma terminal discharge outlet 240. The treated water 250 is sampled atdischarge by a TOC analyzer 260, which adjusts and controls thepersulfate feed pump 170 according to the needs of the system.

FIG. 1B shows AOP 100 implementation in a typical semiconductor UPWproduction system 470 when employed in the production of UPW prior tothe POD 360 and also prior to the POC 380 to produce ultra low level TOC(i.e. <POD level) for critical POU usage 390. FIG. 1B also shows AOP 100implementation when employed in the purification of spent UPW 440 fromsemiconductor fabrication.

Treated reuse UPW 460 can be blended with raw feed water 270 to producethe required blended feed flow 280 to the UPW production system 470.Alternatively, the treated reuse UPW 460 can be blended with UPW at anypoint within the UPW production system 470. The Pretreatment Systemtreats the blended feed flow by combining various technologies, asrequired, for suspended solids reduction, initial organic compoundreduction, chlorine removal and pH adjustment to produce feed water 300with the proper characteristics for efficient production of UPW in theMake-Up System 310. The Make-Up System process typically includes HeatExchange (HX), Ultra-Filtration (UF), Membrane Filtration (MF), 1^(st)Pass Reverse Osmosis (RO), 2^(nd) Pass RO, Electro-deionization (EDI),Ion Exchange (IX), Membrane De-Aeration (MD-A) or Vacuum De-Aeration(VD-A), and UV Sterilization (UV) to produce the required Make-Up waterquality 320 with a flow equal or greater than the total average usage atthe POU (370 plus 390). Make-Up water stored in DI Storage 330 provideslimited backup when the Make-Up System is out of service or when theaverage POU UPW usage exceeds the capacity of the Make-Up System. UPWfrom DI Storage is pumped 340 through the Polish System 350 at a flowrate greater than UPW peak usage at the combined POU. UPW in the PolishSystem is purified using HX, EDI, IX, UV, MF, and UF to produce UPW perPOD 360 quality specifications as required at the non-critical POU 370.Certain critical fab processes 390, such as photolithography, requireUPW with an impurity level less than produced at the POD 360. To meetthis requirement, POU System(s) 410 are installed at the POC(s) to thecritical fab process(es). The POU System can include HX, RO, EDI, IX,MD-A, pressure control, UV, MF, and UF, as required to meet fab-specificUPW specifications at the POC(s). The sum of non-critical and criticalfab UPW usage equals the combined fab UPW usage. UPW not used at thecombined POU is returned 400 to DI Storage. Certain fab UPW usageproduces spent UPW water not economically suitable for reuse 420 (due tohigh levels of suspended solids, chemicals, etc.) that is sent to wastetreatment. Most spent UPW 430 is primarily contaminated with TOC thatcan be purified in a Reuse System 440 and forwarded 460 for blendingwith raw feedwater 270. Water not meeting specifications for blending450 is sent to waste treatment.

The AOP 100 can be employed at any point in the UPW production system470, consisting of the Pretreatment System, the Make-Up System, the DIStorage, and the Polish System.

The AOP 100 in the UPW production system 470 may be located on theproduct stream of the 1^(st) Pass RO. At this point the feedwater to theAOP 100 has significantly reduced levels of suspended solids, ionizedsolids, microorganisms, and TOC, all of which enhance the performance ofthe AOP 100. The TOC in the AOP 100 product should be controlled so thatthe TOC at the POD 360 and non-critical POU 370 is less thanspecification. Product water from AOP 100 is directed to following unitprocesses in the UPW production system 470, where oxidation productsfrom the AOP process are removed.

The AOP 100 can be employed at any point between the POD 360 and the POC380 to critical POU 390 to reduce TOC to the specification required byPOU 390. Additional unit processes, similar to those found in the UPWproduction system 470 may be employed to remove oxidation productsproduced in the AOP 100, or to meet other specifications for the POU 390not achieved with UPW delivered from the POD 360.

The AOP 100 can be employed in the Reuse System 440 to reduce TOC insegregated, spent UPW 430 to produce Reuse UPW 460 suitable for reuse inthe UPW System or for other uses. Suspended solids reduction in thereuse feedwater 430 using MF or UF may be employed to improve theefficiency of the AOP 100. Ionized solids reduction using RO, EDI, or IXin part of, or all of the Reuse UPW 460 may be employed to meet usespecifications of the Reuse UPW.

As an alternative or addition to a feed back signal from a TOC/TDSanalyzer disposed on the effluent discharge, a feed forward signal tothe persulfate addition system may be supplied by a TOC analyzerdisposed on the inlet end of the water to be treated. The performance ofthe reactor is a function of the following design parameters: (1)residence time; (2) reactor radius (light path length); (3) lamp linearenergy density; (4) energy wavelength; (5) persulfate concentration;and, (6) TOC composition and concentration.

The reactor design is selected after determining the amount ofpersulfate that needs to decompose to effect the required TOCdecomposition. The persulfate decomposition fraction and addition rateis established by optimizing the design parameters for capital cost,operating cost and available footprint.

The decomposition of persulfate to sulfate radicals and the subsequentreaction of the radicals with organic compounds is a homogeneous set ofreactions. The longer the fluid retention time in the reactor, thegreater the amount of activating UV light absorbed. Thus, residence timeaffects the fraction of the feed persulfate that will be decomposed and,consequently, the amount of organic material that will be oxidized.

Increasing the reactor radius increases the residence time and increasesthe distance between the lamps and the reactor walls. The incrementalreactor volume further from the lamps is less effective for persulfatedecomposition due to lower photon flux. However, because the light mustpass through more water, more photons are absorbed, resulting in betteruse of the input UV. The effect of increased reactor radius is then afunction of the effective absorption of the water. If the water absorbslittle of the light, then increasing the reactor radius has a largerimpact on performance. The residence time varies as a square of theradius, but because the view factor scales inversely with the distancefrom the lamp, photon flux varies as 1/r. Accordingly, if UV power isrelatively more expensive than tank size, the tank radius should be setso that little UV light reaches the tank walls.

The effect of light energy input, or linear energy density of the lamp,is also straightforward. As more light is added to the reactor morepersulfate will be decomposed. The amount of persulfate decomposedgenerally scales linearly with energy input. Energy input can be variedby changing the number of lamps used and the choice of lamp. Forexample, a standard low pressure mercury lamp, used for both photolysisand biological control, has a 254 nm output of about 0.2 W/cm. Amalgamlamps are available that give 0.4 and 0.6 W/cm. And medium pressuremercury lamps typically give 15 W/cm in the 200-260 nm range.

The wavelength of light employed is also a critical design variable.FIG. 2 graphically shows the absorption spectrum 500 for aqueouspersulfate. As shown in FIG. 2, persulfate absorbs a larger fraction oflight as the wavelength is reduced. At 254 nm very little of the lightis absorbed. Using 220 nm light would result in much more lightabsorption for a given path-length. Adjusting the UV to a wavelengthwhere persulfate absorbs stronger improves performance in situationswhere some fraction of the light is not absorbed before reaching thereactor vessel wall. The extra absorbed light translates directly tomore persulfate decomposed and improved performance. A lower limit onwavelength is set by the water absorption of photons which occursstrongly below ˜190 nm.

For a given reactor design, the TOC decomposition performance depends onthe feed rate of persulfate. The amount of persulfate required for agiven performance depends on: (a) specific chemicals contributing toTOC; (b) concentration of these chemicals; and (c) TOC decompositionperformance required.

The amount of persulfate needed is also affected if there are otherchemicals in the water that absorb UV (lowering the effective quantumefficiency of persulfate degradation) or that are oxidized by sulfateradicals (thus competing with TOC for sulfate radicals.) Generally,cleaner water allows for more efficient TOC control.

The method may be demonstrated by the following examples, which areprovided for purposes of illustration only, and do not limit the scopeof the disclosure described herein.

Example 1

Tests indicate that for a given target chemical the absolute reactionrate is low order in the target chemical concentration. A givenpersulfate feed rate and UV power generates a number of radicals which,over a narrow target chemical concentration, decompose a fixed amount ofthe target compound independent of the concentration of the targetcompound.

FIG. 3 graphically shows the effect of urea concentration on performancefor a fixed residence time and persulfate feed rate 600. The data weregenerated using a plug flow reactor with a 254 nm lamp. The data showthat the absolute amount of urea decomposed at 10 ppb was only twicethat decomposed at 2 ppb. As with other AOPs, some oxidant-to-targetmolar ratio will be required to achieve a required performance. Thisaffect contrasts with many chemical processes where the reaction ratescales proportionally to the target chemical concentration.

These data are an example of using the process to remove a relativelydifficult to oxidize compound from an ultra-pure water stream.

Example 2

A series of tests was conducted to test the stirred tank (CSTR) designconcept with simulated spent rinse water. Isopropanol (IPA) was used asthe target compound since it has been shown to be difficult to decomposeand is a major component of spent rinse water. The objective of thestudy was to determine if 1-5 ppm TOC could be reduced to <5 ppb.

The results 700 of the pilot study are summarized as FIG. 4. The resultscan be organized by the three IPA concentrations examined. Note thatthere is a difference between IPA concentration and TOC concentration;IPA is only 60% carbon so 1.5 ppm IPA is equivalent to 915 ppb TOC.

Low IPA Tests—At the lowest IPA concentration tested (1.5 ppm), thepersulfate addition required to achieve the target effluent TOC isreasonable. The effect of increased additive addition on performance islinear up to 100% IPA decomposition with a single 20 minute residencetime CSTR. By adding a one minute residence time plug flow reactor (PFR)in series after the CSTR, the performance is improved by decomposing theresidual persulfate. In other words, some of the additive is notdecomposed in the CSTR and is passed on and decomposed in the PFR.Additive addition of 75 ppm is sufficient to destroy essentially all ofthe IPA with the two reactors in series.

Moderate IPA Tests—The relationship between persulfate addition and IPAdecomposition is also linear at the moderate TA concentration (2.4 ppm)tested. Nearly 100% decomposition is achieved using 200 ppm persulfateusing the 20 minute residence time CSTR. The additive requirements areincreased somewhat when the residence time of the CSTR is decreased to15 minutes.

High IPA Tests—At the highest IPA concentration (4.9 ppm) the amount ofpersulfate required to achieve the 99+% decomposition requirement issignificant. The relationship between additive addition anddecomposition performance is also not linear. The effect of higherpersulfate concentrations on performance is diminished as 100%decomposition is approached. Although this IPA concentration is higherthan is expected for the intended application, the ability to attainnear complete decomposition for higher IPA concentrations in water givesa desirable flexibility to the process.

Collectively, these tests show that the technology is viable for spentrinse water treatment using a simple CSTR photochemical reactor ofsufficient residence time and modest UV energy input.

The disclosure herein shows that a system directed to treatingsemiconductor process water to reduce total organic compounds in thewater. The system includes a chemical reactor vessel and a persulfateanion addition system upstream of the chemical reactor vessel, andemploys light energy to oxidize the aqueous persulfate. It may be usedto treat pure water for semiconductor manufacturing, and to decomposeTOC to less than 5 ppb, or to below 1 ppb. However, it may also beemployed to treat semiconductor-manufacturing wastewater, and in such animplementation, it is used to decompose TOC to a concentrationsufficiently low to allow reuse of the water. In each implementation,the persulfate feed rate is controlled by a TOC analyzer based on a feedback signal from effluent TOC analysis. Alternatively, it may becontrolled by a feed forward signal from analysis of the TOC in theuntreated feed water. In yet another alternative, it may be controlledby both.

Further, a method is provided for treating semiconductor process waterto reduce total organic compounds, and this method comprises the stepsof (1) providing a source of semiconductor manufacturing water with aTOC concentration higher than required for ultrapure uses; (2) mixingaqueous persulfate anions with the semiconductor manufacturing water ina chemical reactor vessel; (3) exposing the persulfate anion and watermixture to ultraviolet light for a predetermined residence time; and (4)discharging the treated water for further treatment required forultrahigh purity uses. The method may be used when the semiconductormanufacturing water is pure water, and the process may be employed todecompose TOC to less than 5 ppb, or to less than 1 ppb. Furthermore,the method may be used in treating semiconductor manufacturing wastewater, and the process is used to decompose TOC to a concentrationsufficiently low to allow reuse of the water, and further processing maybe effected to remove dissolved solids and dissolved gases.

In effecting the process, the introduction of persulfate into thereaction vessel may be controlled using either a feed back signal fromeffluent TOC analysis, or a feed forward signal from analysis of the TOCin the untreated feed water, or both. In the former case, the TOCanalyzer would be disposed between the source of water to be treated andthe chemical reactor vessel, and in the latter, the TOC analyzer wouldbe disposed anywhere downstream of the chemical reactor vessel,including on the discharge outlet itself or anywhere prior to the pointof use or re-use.

While the particular apparatus and method herein shown and disclosed indetail is fully capable of attaining the objects and providing theadvantages stated herein, it is to be understood that it is merelyillustrative of an embodiment and that no limitations are intendedconcerning the detail of construction or design shown other than asdefined in the appended claims.

Accordingly, the proper scope of the present disclosure should bedetermined only by the broadest interpretation of the appended claims soas to encompass obvious modifications as well as all relationshipsequivalent to those illustrated in the drawings and described in thespecification.

1. A system for treatment of water for use in semiconductormanufacturing, comprising: a source of semiconductor manufacturingwater; a chemical reactor vessel fluidly connected downstream of thesource of semiconductor manufacturing water; a persulfate additionsystem fluidly connected to the chemical reactor vessel, the persulfateaddition system comprising: a persulfate feed tank; and a persulfatefeed pump fluidly connected to the persulfate feed tank and configuredto deliver persulfate to the chemical reactor vessel; a light emittingdevice positioned within the chemical reactor vessel; and a totalorganic carbon analyzer configured to receive an input signal of a totalorganic carbon measurement and configured to provide an output signal tocontrol the persulfate feed pump in response to the input signal.
 2. Thesystem of claim 1, wherein the chemical reactor vessel is selected fromthe group consisting of a continuous stirred tank reactor and a plugflow reactor.
 3. The system of claim 1, wherein the chemical reactorvessel comprises a continuous stirred tank reactor, the system furthercomprising a plug flow reactor fluidly connected downstream of thecontinuous stirred tank reactor.
 4. The system of claim 1, wherein thelight emitting device comprises an ultraviolet lamp.
 5. The system ofclaim 4, wherein the ultraviolet lamp is configured to emit light at afrequency from about 190 nm to about 220 nm.
 6. The system of claim 1,wherein the total organic carbon analyzer is disposed upstream of thechemical reactor vessel.
 7. The system of claim 1, wherein the totalorganic carbon analyzer is disposed downstream of the chemical reactorvessel.
 8. The system of claim 7, wherein the total organic carbonanalyzer is further configured to provide an output signal to increasepersulfate delivered to the chemical reactor vessel in response to aninput signal indicating that the total organic carbon measurementexceeds 5 ppb.
 9. The system of claim 7, wherein the total organiccarbon analyzer is further configured to provide an output signal toincrease persulfate delivered to the chemical reactor vessel in responseto an input signal indicating that the total organic carbon measurementexceeds 1 ppb.
 10. A water treatment system, comprising: a source ofsemiconductor manufacturing water; a make-up system fluidly connecteddownstream of the source of semiconductor manufacturing water; a polishsystem fluidly connected downstream of the make-up system; a point ofuse fluidly connected downstream of the polish system; and an advancedoxidation process system fluidly connected between of the source ofsemiconductor manufacturing water and the point of use, the advancedoxidation comprising: a chemical reactor vessel; a persulfate additionsystem fluidly connected to the chemical reactor vessel; a lightemitting device positioned within the chemical reactor vessel; and atotal organic carbon analyzer configured to receive an input signal of atotal organic carbon measurement and configured to provide an outputsignal to control the persulfate addition system in response to theinput signal.
 11. The system of claim 10, wherein the persulfateaddition system comprises a persulfate feed tank and a persulfate feedpump fluidly connected to the persulfate feed tank and configured todeliver persulfate to the chemical reactor vessel.
 12. The system ofclaim 10, wherein the make-up system comprises at least one of a heatexchanger, an ultra-filtration membrane, a membrane filtration unit, afirst-pass reverse osmosis unit, a second-pass reverse osmosis unit, aelectro-deionization unit, an ion exchange unit, a membrane de-aerationor vacuum de-aeration unit, and an ultraviolet sterilization system. 13.The system of claim 10, wherein the polish system comprises at least oneof a heat exchanger, an electro-deionization unit, an ion exchange unit,an ultraviolet sterilization system, a membrane filtration unit, and anultra-filtration membrane.
 14. The system of claim 10, wherein thesource of semiconductor manufacturing water comprises at least one of: asource of raw feed water; a source of spent ultrapure water; and ablended feed comprising a mixture of the raw feed water and the spentultrapure water.
 15. The system of claim 10, further comprising apretreatment system fluidly connected downstream of the source ofsemiconductor manufacturing water and upstream of the make-up system,wherein the pretreatment system comprises a system selected from thegroup consisting of a suspended solids removal system, an organiccompound reduction system, a chlorine removal system, a pH adjustmentsystem, and a carbon dioxide reduction system.
 16. The system of claim10, further comprising a deionized water storage system fluidlyconnected downstream of the make-up system and upstream of the polishsystem.
 17. The system of claim 10, wherein the make-up system comprisesa first-pass reverse osmosis unit and a second-pass reverse osmosisunit, and wherein the advanced oxidation process system is fluidlyconnected downstream of the first-pass reverse osmosis unit and upstreamof the second-pass reverse osmosis unit.
 18. The system of claim 10,wherein the advanced oxidation process system is fluidly connectedupstream of the polish system.
 19. The system of claim 10, wherein theadvanced oxidation process system is positioned within the polishsystem.
 20. The system of claim 10, wherein the advanced oxidationprocess system is fluidly connected downstream of the polish system. 21.The system of claim 10, wherein the light emitting device comprises anultraviolet lamp configured to emit light at a frequency from about 190nm to about 220 nm
 22. The system of claim 10, wherein the total organiccarbon analyzer is disposed upstream of the chemical reactor vessel. 23.The system of claim 10, wherein the total organic carbon analyzer isdisposed downstream of the chemical reactor vessel.
 24. The system ofclaim 23, wherein the total organic carbon analyzer is furtherconfigured to provide an output signal to increase persulfate deliveredto the chemical reactor vessel in response to an input signal indicatingthat the total organic carbon measurement exceeds 5 ppb.
 25. The systemof claim 23, wherein the total organic carbon analyzer is furtherconfigured to provide an output signal to increase persulfate deliveredto the chemical reactor vessel in response to an input signal indicatingthat the total organic carbon measurement exceeds 1 ppb.